Seasonal abundance, vertical distribution and life history traits of Mediterranean mud shrimp Upogebia pusilla (Decapoda: Gebiidea) on the Slovenian coast

We studied seasonal abundance, vertical distribution and life history traits of the Mediterranean mud shrimp (Upogebia pusilla) in the mediolittoral zone in Slovenia. At two localities (Strunjan and Lazaret), quantitative samples from three plots (1 m2 each) at (0 cm), below (-50 cm) and above (+50 cm) mean water level were taken once every two months, in alternation. A set of parameters was also recorded, including vegetation cover, sediment type, air and sea temperature, pH, salinity and oxygen levels. Highest abundance was recorded during the warm period of the year, with peak abundance in June 2012 (21 % of total sample). Lowest plots were always occupied with the highest densities of mud shrimps. Males dominated during the winter while ovigerous females reached the peak in June (>40 % of all animals). In June at least 2/3 of females were ovigerous. Estimated mean incubation period was 31 days. We determined four periods in relation to the species’ reproductive activity. Early reproductive period (April) was characterised by emergence of first ovigerous females, while main reproductive period (May–July) was characterised by peak of reproduction. In post-reproductive (August–October), and non-reproductive (November–March) periods, no ovigerous females or newly hatched offspring were recorded.